The invention relates to a thermodynamic engine employing superheated vapor to generate kinetic energy.
The invention proceeds from WO 02/31320 A1. The cited document describes a thermodynamic engine for an internal combustion engine which operates according to the Rankine cycle process. The thermodynamic engine is characterized by the fact that it comprises two parallel Rankine cycle processes, in each of which a pump first transports a liquid through a heat exchanger located on an exhaust gas train of an internal combustion engine, the liquid being evaporated, further transported into a decompression device in which the superheated vapor drives a vane pump, and further transported into a condenser in which the residual vapor is condensed. The liquid then flows back through the same circuit. To improve the efficiency of the thermodynamic engine, liquids with different boiling points are used in the circuits. In a proposed embodiment, the circuit with its heat exchanger located closer to the internal combustion engine receives the liquid having the higher boiling temperature. This circuit is a high-temperature circuit, whereas the second circuit is a low-temperature circuit. In order to maintain the efficiency of the high-temperature circuit at a high level, its pump is a variable feed pump.
Although the efficiency of the thermodynamic engine is improved by the above-mentioned measures, the internal combustion engine still releases a large amount of unused thermal energy to the surroundings.
The object of the present invention is to further increase the efficiency of a thermodynamic engine in conjunction with an internal combustion engine.
This object is achieved according to the invention by the fact that, in addition to the waste heat which the internal combustion engine dissipates through the exhaust gas train, use is also made of the waste heat from the coolant circuit for the internal combustion engine in order to regulate the temperature of the working medium in the low-temperature circuit, i.e., the first working medium. “Temperature regulation” is understood to primarily mean heating. The liquid first working medium preheated or heated in this manner is subsequently pumped from a collection container by a pump and is injected via an injection device back into the low-temperature circuit. The injection occurs in the first heat exchanger in order to allow the preheated first working medium to be re-evaporated as quickly as possible in the low-temperature heat [sic] circuit, independent of the available heat and the load requirement. The excess pressure thus produced in the low-temperature circuit is converted to additional kinetic energy in a decompression device. As a result of the temperature regulation, i.e., heating, of the first working medium with the assistance of the coolant circuit for the internal combustion engine, the quantity of heat released by the internal combustion engine is utilized much better for producing mechanical energy. With the proper dimensioning of the thermodynamic engine, a radiator present in the coolant circuit may be advantageously reduced in size or even omitted. The dissipation of heat from the internal combustion engine via the coolant then occurs exclusively in the first collection container in the low-temperature circuit. As a result of the additional possibilities for injection in the low-temperature circuit, very short reaction times, i.e., response times, can be achieved for the decompression device. In principle, separation of the two circuits allows great flexibility in the operating strategy. To increase this benefit even further, an additional heating device is provided in the high-temperature circuit by which the second working medium already in the vapor state is further heated very rapidly and, thus, is superheated. The overall system attains a higher efficiency through the proposed concept. Further advantageous embodiments are the subject matter of the subclaims.
It is also possible to temporarily store the first working medium, which is collected in the first collection container, in both the gaseous and liquid phases. As a result of this phase separation, it is possible to heat the gaseous portion and the liquid portion separately. Whereas the gaseous first working medium is supplied via the first heat exchanger for the decompression device, the working medium in the liquid phase is injected via the injection device back into the low-temperature circuit in the vicinity of the first heat exchanger, evaporated there, and sent to the decompression device. This measure increases the dynamics of the thermodynamic engine.
The low-temperature circuit achieves a further increase in efficiency by additionally regulating the temperature of the first working medium in the first collection container, using the residual heat from the second working medium coming from the decompression device. By use of this measure, the energy still stored in the second working medium, after the decompression device, is also advantageously released to the low-temperature circuit before the second working medium is cooled and liquefied in a condenser.
A second collection container for collecting the liquefied second working medium may also be provided in the high-temperature circuit as well. Further, advantageous use is made of the second collection container to preheat the second working medium with the cooling water from the internal combustion engine before the second working medium is introduced into the second heat exchanger. In this configuration, the coolant for the internal combustion engine is first passed through the first collection container in the low-temperature circuit and then through the second collection container to make use of the residual thermal energy, still stored in the coolant, for preheating or heating of the high-temperature circuit. For this proposed embodiment, in the optimum system design a coolant heat exchanger that is present can be either reduced in size or omitted.
The heating device further may be operated either by electrical power and/or by a fuel, which preferably is the same fuel as for the internal combustion engine. As a result of this measure, a single fuel tank is sufficient, and additional fuels are not necessary. For an internal combustion engine operated on gasoline, there is the option to use a gasoline heating device, and for a diesel engine, to use a diesel heating device, and for a gas-operated engine, to use a gas heating device. Very brief heating times are achievable when an electric heating device is used.
To achieve superheating of the second working medium, the heating device may be radially situated around the exhaust gas system, preferably between two catalytic cleaning devices. This arrangement once again makes optimum use of the thermal energy from the exhaust gas in order to superheat the high-temperature circuit. Energy is withdrawn from the exhaust gas in such a way that the catalytic cleaning device closer to the engine, the precatalyst, quickly comes to operating temperature in order to clean unwanted substances from the exhaust gas. The catalytic cleaning device farther from the engine, the main catalyst, is situated in the direction of flow downstream from the heating device, and is thus substantially protected from overheating. This protection is also provided by installing the heating device, which at the same time is a heat exchanger, upstream from the main catalyst.
The first and second heat exchangers also may be situated downstream from the second catalytic cleaning device to avoid withdrawing too much thermal energy from the exhaust gas upstream from the catalytic cleaning device, and thus eliminating the catalytic effect due to low temperature. The optimum overall efficiency is achieved by the proposed arrangement of the two catalytic cleaning devices, the heating device, and the second and first heat exchangers.
By regulating the volumetric flow of the working media through the decompression device for the low- and high-temperature circuits, it is possible to adapt the operating conditions of the thermodynamic engine to the operating conditions of the internal combustion engine. At full load operation of the internal combustion engine, i.e., at high to maximum power release, the maximum volumetric flow of the working media is set to achieve the optimum energy utilization. At partial load operation or stop-and-go operation, i.e., at average to low power release, the volumetric flow of the working media is correspondingly reduced.
A partial vacuum may be created in the condenser, using the arrangement of an additional pump in the low-temperature circuit between the condenser and the first collection container. This partial vacuum causes the first working medium to liquefy at even lower temperatures and subsequently be further pumped into the first collection container. The efficiency of the low-temperature circuit is improved even more by use of the third pump.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.